Lighting devices that generate collimated or near-collimated light beams are used to provide lighting for live performances and special events and for illuminating tall structures. Such lighting devices conventionally use a xenon arc lamp as a light source and a large, deep parabolic reflector to define the direction and beam angle of the light beam. Although xenon arc lamps generate high intensities of white light in a small volume, their efficiency is poor and their service life short. A 1000-watt lamp may only produce 35 lumens per watt of electrical energy and have a service life of only a few thousand hours.
Another disadvantage of the xenon arc-based lighting devices is the reduction in performance that occurs as a result of dirt accumulating on the optical surfaces. This accumulated is compounded by the use of forced-air cooling in such lighting devices. A xenon arc-based light source has at least four surfaces where dirt can accumulate and reduce the light output. Only a small amount of dirt on any of these 4 surfaces significantly reduces the output of the lighting device.
The large, deep parabolic reflector used in a conventional collimated lighting device has a low light collection efficiency. A substantial fraction of the light generated by the xenon arc lamp exits the lighting device through the open end of the parabolic reflector and does not contribute to the collimated beam formed by the light incident on the reflector.
Light emitting diodes (LEDs) have also been used as the light source in lighting devices that output collimated or near-collimated light beam, but challenges remain in efficiently directing the substantially omnidirectional light generated by an LED into a collimated light beam.